Information AboutProteins |
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| molecular biology | |
| nutrition | |
| proteins | |
| proteomics | |
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A protein (from the Greek ''protas'' meaning "''of primary importance''") is a complex, high-molecular-mass, Organic Compound that consists of Amino Acid s joined by Peptide Bond s. Proteins are essential to the structure and function of all living Cells and Virus es. Different proteins perform a wide variety of biological functions. Some proteins are Enzyme s, which catalyze chemical reactions. Other proteins play structural or mechanical roles, such as those that form the struts and joints of the Cytoskeleton , which is like a system of Scaffolding within a cell. Still more functions filled by proteins include Immune Response and the storage and transport of various Ligand s. Proteins are a class of bio- Macromolecules , alongside Polysaccharide s, Lipid s, and Nucleic Acid s, that make up the primary constituents of biological Organism s. Proteins are essentially Polymer s made up of a specific sequence of Amino Acids . The details of this sequence are stored in the code of a Gene . Through the processes of Transcription and Translation , a cell reads the genetic information and uses it to construct the protein. In many cases, the resulting protein is then chemically altered (post-translational modification), before becoming functional. It is very common for proteins to work together to achieve a particular function, and often physically associate with one another to form a Complex . In nutrition, proteins are broken down through Digestion back into free Amino Acids for the Organism , including those the organism may not be able to synthesize itself. Proteins are among the most actively-studied Molecule s in Biochemistry , and were discovered by Jöns Jakob Berzelius in 1838. PROPERTIES OF PROTEIN Components and synthesis Proteins are polymers built from 20 different L-alpha- Amino Acid s. Proteins are assembled from amino acids using information present in Gene s. Genes are Transcribed into RNA , RNA is then subject to post-transcriptional modification and control, resulting in a mature MRNA that undergoes Translation into a protein. mRNA is translated by Ribosome s that match the three-base Codon s of the mRNA to the three-base anti-codons of the appropriate TRNA . The enzyme Aminoacyl TRNA Synthetase catalyzes the addition of the correct amino acid to their tRNAs. The two ends of the amino acid chain are referred to as the Carboxy Terminus (C-terminus) and the Amino Terminus (N-terminus) based on the nature of the free group on each extremity. Structure See Also: Protein structure Proteins Fold into unique 3-dimensional structures. The shape into which a protein naturally folds is known as its Native State , which is determined by its sequence of amino acids. Thus, proteins are their own polymers, with amino acids being the monomers. Biochemists refer to four distinct aspects of a protein's structure:
In addition to these levels of structure, proteins may shift between several similar structures in performing their biological function. In the structures are usually referred to as " Conformation s," and transitions between them are called conformational changes. The process by which the higher structures are formed is called Protein Folding and is a consequence of the primary structure. The mechanism of protein folding is not entirely understood. Although any unique polypeptide may have more than one stable folded conformation, each conformation has its own Biological Activity and only one conformation is considered to be the active one. Protein regulation Various molecules and ions are able to bind to specific sites on proteins. These sites are called Binding Site s. They exhibit Chemical Specificity . The particle that binds is called a Ligand . The strength of ligand-protein binding is a property of the binding site known as Affinity . Since proteins are involved in practically every function performed by a cell, the mechanisms for controlling these functions therefore depend on controlling protein activity. Regulation can involve a protein's Shape or Concentration . Some forms of regulation include:
Diversity Proteins are generally large molecules, having Molecular Mass es of up to 3,000,000 (the muscle protein Titin has a single amino acid chain 27,000 subunits long) however protein masses are generally measured in KiloDaltons (kDa). Such long chains of amino acids are almost universally referred to as proteins, but shorter strings of amino acids are referred to as "polypeptides," " Peptide s" or rarely, "oligopeptides". The dividing line is undefined, though "polypeptide" usually refers to an amino acid chain lacking tertiary structure which may be more likely to act as a Hormone (like Insulin ), rather than as an enzyme (which depends on its defined tertiary structure for functionality). Proteins are generally classified as soluble, filamentous or membrane-associated (see , Actin , Collagen and Keratin , all of which are important components of Skin , Hair , and Cartilage . Another special class of proteins consists of Motor Protein s such as Myosin , Kinesin , and Dynein . These proteins are "molecular motors," generating physical force which can move Organelle s, Cell s, and entire Muscle s. (IgG), Hemoglobin , Insulin (a hormone), Adenylate Kinase (an enzyme), and Glutamine Synthetase (an enzyme).]] ROLE OF PROTEIN Functions Proteins are involved in practically every function performed by a cell, including regulation of cellular functions such as Signal Transduction and Metabolism . Life, chemically speaking, is nothing but the function of proteins, although the information to make a unique protein resides, passively, in the DNA. The protein involved in functions control almost all the molecular processes of the body. Proteins are the actors, that ''do'' everything that happens within us. Although proteins do almost everything in an organism, several particularly important functional classes may be recognized: # Enzymes , that catalyze all of the reactions of metabolism; # structural proteins, such as Tubulin , or Collagen ; # regulatory proteins, such as Transcription Factors or cyclins that regulate the cell cycle; # signalling molecules or their receptors such as some Hormones and their receptors; # defensive proteins, which can include everything from Antibodies of the Immune System , to toxins (e.g., Dendrotoxin s of snakes), to proteins that include unusual amino acids like Canavanine . Nutrition > In nutrition, proteins are broken down through Digestion , which begins in the stomach. Proteins are broken down by proteases into smaller Polypeptide s to provide Amino Acids for the Organism , including those the organism may not be able to synthesize itself. Pepsinogen is converted into the enzyme Pepsin when it comes into contact with Hydrochloric Acid . Pepsin is the only Proteolytic Enzyme that digests Collagen , the major protein of connective tissue. Most protein digestion takes place in the Duodenum with the overall contribution from the stomach being small. Almost all protein is absorbed when it reaches the Jejunum with only 1% of ingested protein left in the Feces . Some amino acids remain in the epithelial cells and are used for synthesis of new proteins, including some intestinal proteins, constantly being digested, recycled and absorbed from the Small Intestine . Benefits in the diet Protein is an important Macronutrient to the human diet, supplying the body's needs for Amino Acid s, the building blocks of proteins. Mammals cannot synthesize all 20 amino acids, so protein from the diet is necessary to acquire those that cannot be synthesized, known as Essential Amino Acid s (8 in human). The exact amount of dietary protein needed to satisfy these requirements for humans, known as an RDA may vary widely depending on age, sex, level of physical activity, and medical condition. Protein deficiency can lead to symptoms such as fatigue, Insulin resistance, Hair loss, loss of hair Pigment , loss of Muscle mass, low body temperature, Hormonal irregularities, as well as loss of skin elasticity. Severe protein deficiency, encountered only in times of Famine , is fatal, due to the lack of material for the body to construct its own proteins (see Kwashiorkor ). Potential risks Some suspect excessive protein intake is linked to several problems:
It is assumed by researchers in the field, that excessive intake of protein forces increased calcium excretion. If there is to be excessive intake of protein, it is thought that a regular intake of calcium would be able to stablilise, or even increase the uptake of calcium by the small intestine, which would be more beneficial in older women Kerstetter, J. E., O'Brien, K. O., Caseria, D.M, Wall, D. E. & Insogna, K. L (2005) ''"The impact of dietary protein on calcium absorption and kinetic measures of bone turnover in women"''. ''J Clin Endocrinol Metab'' (2005) Vol 90, p26-31, .. Proteins are often progenitors in Allergies and Allergic Reaction s to certain Food s. This is because the structure of each form of protein is slightly different; some may trigger a response from the immune system while others remain perfectly safe. Many people are allergic to Casein , the protein in milk; Gluten , the protein in wheat and other grains; the particular proteins found in Peanut s; or those in Shellfish or other Seafood s. It is extremely unusual for the same person to adversely react to more than two different types of proteins, due to the diversity between protein or amino acid types. STUDYING PROTEINS Proteins are sensitive to their environment. They may only be active in their Native State , over a small PH range, and under solution conditions with a minimum quantity of Electrolyte s. A protein in its native state is often described as ''folded''. A protein that is not in its native state is said to be Denatured . Denatured proteins generally have no well-defined Secondary Structure . Many proteins denature and will not remain in solution in Distilled Water . One of the more striking discoveries of the 20th century was that the native and denatured states in many proteins were interconvertible, that by careful control of solution conditions (by for example, Dialyzing away a denaturing chemical), a denatured protein could be converted to native form. The issue of how proteins arrive at their native state is an important area of biochemical study, called the study of Protein Folding . Through Genetic Engineering , researchers can alter the sequence and hence the structure, "targeting" , susceptibility to regulation and other properties of a protein. The genetic sequences of different proteins may be spliced together to create "chimeric" proteins that possess properties of both. This form of tinkering represents one of the chief tools of cell and molecular biologists to change and to probe the workings of cells. Another area of protein research attempts to engineer proteins with entirely new properties or functions, a field known as Protein Engineering . Protein-protein interactions can be Screened for Two-hybrid Screening . HISTORY The first mention of the word ''protein'' was from a letter sent by Jöns Jakob Berzelius to Gerhardus Johannes Mulder on 10. July 1838, where he wrote: : «Le nom protéine que je vous propose pour l’oxyde organique de la fibrine et de l’albumine, je voulais le dériver de πρωτειοξ, parce qu’il paraît être la substance primitive ou principale de la nutrition animale.» Translated as: : "The name protein that I propose for the organic oxide of Fibrin and Albumin , I wanted to derive from [the Greek word] πρωτειοξ, because it appears to be the primitive or principal substance of animal nutrition." Investigation of proteins and their properties had been going on since about 1800 when scientists were finding the first signs of this, at the time, unknown class of organic compounds. SEE ALSO
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